Sorry, that is just not true. My late first wife and I went into full-time Christian service as 24-hours-a-day, ten-days-per-shift house parents for five mentally handicapped adult women with the same stars in our eyes that you seem to have. We were going to be wonderfully kind and loving, and the mentally handicapped women were going to respond accordingly. We were going to be one big happy Christian household. We had a rude, rude, RUDE awakening. It was the closest to Hell I ever expect to be. I'll spare you the details, but I concluded that do to this job properly requires a near-saint who has genuinely been called by God for this particular service and can withstand conditions that are pretty much the equivalent of warfare.
After this, I served for almost 15 years as the attorney for an agency that obtained court orders for seriously mentally ill adults to be involuntarily committed for treatment. The cases were almost invariably gut-wrenching. Loving mothers, fathers, husbands, brothers and sisters absolutely could not cope with these people. My wife now, an extremely devout Christian, was in charge of inspecting homes for the mentally handicapped in the Soviet Union, and her experiences were exactly the same as mine.
Any notion that the mentally ill are sweeties who recognize and respond to Spirit-filled kindness is Pollyannaish in the extreme and typically held by people who have little experience with these unfortunate folks. Some of them are sweeties and will respond, of course, but this is true of any segment of the population. It is an extremely challenging situation, as challenging to a Christian perspective as the so-called Problem of Evil.
Do you believe that what the doctors call "mentally ill", are really those who are oppressed by the devil, and even possessed in some cases?
JLB